The present invention relates to a positive working light-sensitive composition which makes it possible to form a presensitized plate for use in making a lithographic printing plate (hereunder referred to as "PS plate"), proof sheets for process printing, figures for overhead projectors or fine resist patterns required for making integrated circuits (IC) of semiconductor elements; components or intermediates useful for the preparation of the positive-working light-sensitive composition; and a process for the preparation of the components or intermediates.
As so-called positive working light-sensitive materials which are made soluble by irradiating with actinic rays, for instance, in making lithographic printing plates, there have been known o-quinonediazide compounds and these compounds have practically been utilized widely for preparing PS plates or the like. Such o-quinonediazide compounds are disclosed in various publications inclusive of U.S. Pat. Nos. 2,766,118; 2,767,092; 2,772,972; 2,859,112; 2,907,665; 3,046,110; 3,046,111; 3,046,115; 3,046,118; 3,046,119; 3,046,120; 3,046,121; 3,046,122; 3,046,123; 3,061,430; 3,102,809; 3,106,465; 3,635,709; and 3,647,443.
These o-quinonediazide compounds are decomposed by irradiation with actinic rays to form 5-membered carboxylic acids and they are thus made alkali-soluble. In these applications of the light-sensitive material, such properties of the compounds are utilised. However, their light-sensitivity is insufficient. This problem arises because it is difficult to optically sensitize the o-quinonediazide compounds and their quantum yield essentially never exceeds 1. Moreover, the wave length used for exposing the same is limited to a specific one and, therefore, tolerance with respect to light sources is narrow. In other words, it is difficult to impart resistance to incadescent rays to the composition. In addition, the absorption of light in Deep-UV region ranging from about 200 to 300 nm is great and thus it is not suitable for applications in which light of short wave length is used to enhance the resolution of a photoresist.
Many attempts have been made to improve the light-sensitivity of light-sensitive compositions containing o-quinonediazide compounds. However, it is very difficult to improve the light-sensitivity while maintaining the development tolerance during development. For instance, examples of such attempts are disclosed in Japanese Patent Publication for Opposition Purpose (hereunder referred to as "J. P. KOKOKU") No. Sho 48-12242, Japanese Patent Un-examined Publication (hereunder referred to as "J. P. KOKAI") No. Sho 52-40125 and U.S. Pat. No. 4,307,173.
Recently, there have been proposed some positive working light-sensitive compositions free of o-quinonediazide compounds. One example thereof comprises a polymeric compound having o-nitrocarbinol ester groups as disclosed in J. P. KOKOKU No. Sho 56-2696. However, such a composition does not provide high sensitivity for the same reasons as those discussed above in connection with o-quinonediazide compounds.
Separately, there have been proposed methods to improve light-sensitivity using a light-sensitive system which is catalytically activated, wherein a known principle is used that a photolytically generated acid causes a second reaction which makes resist in exposed areas soluble. Examples of the methods include combinations of photolytically acid producing compound and acetal or 0- or N-acetal compound (J. P. KOKAI No. Sho 48-89003), orthoester or amideacetal compound (J. P. KOKAI No. Sho 51-120714), polymer having in the main chain acetal or ketal groups (J. P. KOKAI No. Sho 53-133429), enolether compound (J. P. KOKAI No. Sho 55-12995), N-acylimino carbonic acid compound (J. P. KOKAI No. Sho 55-126236), polymer having in the main chain orthoester groups (J. P. KOKAI No. Sho 56-17345), silyl ester compound (J. P. KOKAI No. Sho 60-10247), and silyl ether compound (J. P. KOKAI Nos. Sho 60-37549 and 60-121446). Since quantum yield principally exceeds 1 in these combinations, high light-sensitivity is realized. However, there are such problems as storage stability over time, and change in sensitivity during the time between exposure to light and development.
There have been also proposed systems which are stable over time at room temperature but are decomposed by heat in the presence of an acid to become alkali-soluble. Examples of such systems include a combination of a compound which produces an acid upon exposure to light and secondary or tertiary carbon (e.g. t-butyl or 2-cyclohexenyl) ester or carbonic acid ester compound disclosed in J. P. KOKAI Nos. Sho 59-45439, 60-3625, 62-229242, and 63-36240, Polym. Eng. Sci., vol. 23, page 1012, (1983), ACS. Sym., vol.242, page 11 (1984), Semiconductor World (1987), November, page 91, Macromolecules, vol. 21, page 1475 (1988) and SPIE, vol. 920, page 42 (1988). In fact, these systems are good in storage stability over time and small in sensitivity change over time after exposure to light. However, they are low in resistance to oxygen plasma when they are used as resist materials for semiconductor.
On the other hand, as pattern-forming methods used in making electronic parts such as semiconductor elements, magnetic bubble memories and integrated circuits, there have been widely employed methods in which a photoresist sensitive to ultraviolet and visible rays. The photoresists are classified into two groups, one of which is negative working type ones whose exposed portions are made insoluble in a developer by irradiating with light, and the other of which is positive working ones whose exposed portions are, on the contrary, made soluble in a developer. The negative working type ones are superior in sensitivity to the positive working ones and adhesion to a substrate and resistance to chemicals required in wet etching are also excellent. Therefore, the use of negative working resists is one of the mainstreams of photolithography. However, the line width and the distance between lines of patterns become smaller as the degree of integration of semiconductor elements and the packaging density thereof are increased. In addition, dry etching techniques have been adopted as a means for etching substrates. Thus, the photoresists should have high resolution and high resistance to dry etching. For this reason, positive working photoresists are mainly utilized recently. In particular, there have been exclusively used alkali developable positive working photoresists mainly composed of alkali-soluble novolak resins as disclosed in J. C. Strieter, Kodak Microelectronics Seminar Proceedings, 1976, p. 116, since they are excellent in sensitivity, resolution and resistance to dry etching.
However, it is required to further scale down the size of patterns to thus achieve more higher packaging density and degree of integration accompanied by the recent increase in multifunctionality and high functionality of electronic devices.
More specifically, the size of integrated circuits in their transversal direction is greatly reduced, but the size thereof in the longitudinal direction cannot be reduced so much. Therefore, the ratio of the height of the resist patterns to the width thereof is correspondingly increased. For this reason, it becomes very difficult to restrict the change in size of the resist patterns on a semiconductor wafer having a complicated stepped structure as the scale down of patterns proceeds. In addition, various methods for exposure suffer from problems as the scale down in the minimum size of patterns. For instance, the exposure by means of light causes interference effect due to light reflected by the stepped portions of the substrate which greatly affects dimensional accuracy. On the other hand, in the exposure by means of an electron beam, the ratio of the height to the width of fine resist patterns cannot be increased because of the proximity effect caused due to backscattering of electrons.
It is found that most of these problems can be eliminated by the use of a multilayered resist system. The multilayered resist system is summarized in Solid State Technology, 74 (1981) and a variety of investigations on the multilayered resist system have been reported. In general, the multilayered resist methods are classified into triple layer resist method and double layer resist method. The triple layer resist method comprises applying an organic film for leveling onto the surface of a stepped substrate, and then applying thereto an inorganic intermediate layer and a resist layer in this order; patterning the resist layer, dry etching the inorganic layer using the patterned resist layer as a mask, and finally patterning the organic leveling layer by 0.sub.2 RIE (reactive ion etching) technique using the inorganic layer as a mask to form a desired pattern on the stepped substrate. The investigation of this method has been started from earlier stage since it can essentially utilize techniques conventionally known, but it requires the use of very complicated processes, or since these layers, i.e., an organic film, an inorganic film and an organic film which differ in physical properties from each other are superposed, the intermediate layer is liable to cause cracks or to form pinholes. Contrary to the triple layer resist method, the double layer resist method utilizes a resist having properties of both resist and inorganic intermediate layers in the triple layer resist method, more specifically a resist resistant to oxygen plasma etching and thus the formation of cracks and pinholes can be suppressed. Further, since the number of layers are reduced from 3 to 2, the process can be simplified. However, a conventional resist can be used as the upper resist in the triple layer resist method while, in the double layer resist method, it is required to newly develop a resist excellent in resistance to oxygen plasma.
Under such circumstances, there has been required to develop a highly sensitive positive working photoresist having a high degree of resolution which is excellent in resistance to oxygen plasma and can hence be used as an upper resist in the double layer resist method or the like, in particular an alkaline developable resist which can be used without changing the processes currently employed.
As such a resist, there have been proposed light-sensitive compositions comprising a combination of a conventional o-quinonediazide light-sensitive material and a silicone polymer such as polysiloxane or polysilmethylene which is made alkali-soluble, for instance, those disclosed in J. P. KOKAI Nos. Sho 61-256347, Sho 61-144639, Sho 62-159141, Sho 62-191849, Sho 62-220949, Sho 62-229136, Sho 63-90534 and Sho 63-91654 and U.S. Pat. No. 4,722,881.
All these silicone polymers are made alkali soluble by introduction of phenolic OH group or silanol group (.tbd.Si--OH). The introduction of phenolic groups are very difficult and silicone polymers having silanol groups are not always stable over time.
Examples of resists not having orthoquinonediazide compound include a light-sensitive composition comprising a combination of a polysiloxane/carbonate block copolymer and an effective amount of an onium salt disclosed in J. P. KOKAI No. Sho 62-136638, silicone polymer having nitrobenzylphenylether groups disclosed in J. P. KOKAI No. Sho 63-146038. However, it is very difficult to produce these polymers. Further, alkali solubility of the polymers exposed to light is not sufficient.